Hadrian's Temple

There is often a disparity between the significance a building had in Roman times and its importance to us now as a witness to those times. For example, in the Roman Forum the best preserved temple is that of Antoninus and Faustina: of a dozen more imposing shrines in the Forum there remains little or nothing. Nary a trace is left in situ of the
Temple of Jupiter Capitoline (although large blocks of stone may be seen in the Capitoline Museums that have been identified by scholars as belonging to the building), yet we have the Temple of Portunus pretty much the way it was.

The Pantheon is a wonderful exception to this unfortunate rule. Conceived as a major monument when Roman architecture was at its zenith, willed by the highest political authorities, and centrally located — it has survived essentially intact.

The Pantheon was intended to honor the highest gods of the Roman religion. Despite the obviousness of its name, however, it was probably not a temple to "all the gods": nothing is simple, and in fact no one knows who exactly was worshipped here — and if you have read otherwise, your modern author, who was not there, will have to slug it out with a 3c Roman senator, who was, and who explicitly says that the reason for the name is a matter of conjecture
(Cassius Dio, 53.27.2). The arrangement of the interior, with its seven altars, has suggested to some the gods of the seven planets, which might also account for the temple's central opening to the sky. A note for the astronomically unwary, however: no planet can, or could then, ever be seen thru the oculus. The ecliptic lies too low.

To be even more frank, no one knows that much about Roman religion; when in our own day the exact meaning of prayer, for example, is subject to many sometimes conflicting interpretations even within a single monotheistic religion, we can easily imagine our ignorance as to what it meant to build a temple to the all-high gods. An unsatisfyingly vague awareness of numen or divine mystery in its multiple forms is the best we can do: just maybe, by the sheerest accident, that in fact is the meaning of this spherical building open to the sky; but I would not want to project it into the mind of any Roman.

What we can know is what we ourselves see, or what ancient writers tell us: first built in around 25 B.C. by Agrippa (we may think of him as Augustus's vice president), within less than 150 years the Pantheon had been devastated by two fires, and Hadrian saw fit to rebuild it and call that a restoration. While no one knows what the original building looked like, the consensus is that Hadrian's building is nothing like it: welcome to the mystifying world of archaeology.

Once the particular gods had died in whose honor the monument was built, the building stood intact yet apparently unused — no one knows exactly — until the visit from Constantinople to Rome of a thoroughly detestable man, the briefly reigning emperor Phocas, who gave it to the Catholic church. Sensibly, the church preserved it, consecrating it on May 13, 609 ad omnes Martyres, that is, to the thousands of Christians slaughtered thruout the empire during the death throes of the old religion: so although the cultural face of God has changed, the Pantheon is still now a place of worship.

It is in our own age, sadly, that the numen seems to be dying. I once saw two young women wander into the temple slurping on ice cream cones. They were stopped at the door by a priest, but I can't fault them: what were they to make of the fair-like atmosphere
(see this amusing example on the square in front of the church)
and the constant throngs of flash-popping tourists — including of course yours truly?

If you've been scouring the Web for some good basic information and no nonsense, the "Pantheon" entry in
Platner and Ashby's Topography of Ancient Rome
provides a fairly thorough scholarly overview; to which I've added photos of the interior.

A small page, with a couple of photographs, on the famous
doors, which date to the 2c A.D. although with some restoration. This page should be filled out fairly soon.

For the more studious, some good basic topographical and art history information is immediately available:
Christian Hülsen's article on this church
in Le Chiese di Roma nel Medio Evo, linked to 2 further important texts — Armellini's Le Chiese di Roma and the article in the 1763 edition of Filippo Titi's guidebook.

Images with borders lead to more information.
The thicker the border, the more information.
(Details here.)